In vitro mouse kidney differentiation will be used as an experimental system to elucidate mechanisms involved in the control of tubulogenesis. The relationship between tubular differentiation and function will be analysed using morphological, cytological and biochemical criteria. The synthesis of specific proteins during tubulogenesis will be investigated. Finally, the nature of the extrinsic factors operating during kidney tubulogensis will be established by isolating and purifying material from inductively active brain. The mechanisms of action of such material will be analysed.